Objective: The purpose of this study was to find out whether the effects of thermal stress on plasma catecholamines and plasma renin activity are altered by pregnancy.
Study design: Nonpregnant (n = 15) and pregnant (13 to 14 weeks, n = 23; 36 to 37 weeks, n = 23) healthy women were examined. Samples were taken before the exposure, in the heat chamber (70 degrees C), and during the recovery. The BMDP statistical software was used.
Results: The concentration of epinephrine in plasma increased significantly only in the nonpregnant group. The epinephrine concentrations in the pregnancy groups increased most in the subjects who felt discomfort during or after the exposure. Plasma norepinephrine concentrations increased without significant differences between the groups. Plasma renin activity increased in each group, but the increases were significantly lower in the pregnancy groups as compared with the nonpregnant group.
Conclusions: Pregnancy does not alter the thermally induced increase in norepinephrine release. The adrenaline response is mostly dependent on the mental discomfort. The plasma renin activity response to thermal stress is blunted during pregnancy.